The present invention relates generally to electrical cable connectors and relates particularly, but not exclusively, to separable connector modules for connecting together the operating components of an underground power distribution system by means of shielded electrical cable.
Separable connector assemblies for underground power distribution cable, or shielded cable, are watertight when assembled and may be readily separated into two or more units to break a cable connection. As such units are available separately commercially for various reasons and are individually subject to special design considerations, they are commonly referred to as "modules". Thus, a connection includes two or more matching modules assembled together.
One type of separable connector commonly used is known as a "rod and bore" type. A bore connector module having a receiving bore in a shielded, insulating housing and a grasping contact member in the bore receives a matching rod connector module having rod contact which is inserted in the bore and grasped by the bore contact member. Examples of this type of connector are described, for example, in the following U.S. Patents:
U.s. pat. No. 3,513,437 issued 19 May 1970 to W. A. Morris PA1 U.s. pat. No. 3,542,986 issued 24 Nov. 1970 to E. J. Kotski PA1 U.s. pat. No. 3,551,587 issued 29 Dec. 1970 to R. F. Propst, and PA1 U.s. pat. No. 3,587,035 issued 22 June 1971 to E. J. Kotski.
It is desirable to be able to operate such connectors while their cables are electrically active to interrupt the power. As the cables are generally carrying power at a voltage on the order of thousands of volts, separation of the contacts of the connector on a live cable results in the formation of an electric arc between the contacts. The arc will, unless promptly extinguished, eventually strike a ground plane such as the grounded shielding of the modules, and create a direct line-to-ground fault.
In present connectors, the bore is lined with ablative material and the rod is provided with an ablative arc follower of ablative material, a material which generates arc-extinguishing gases when subjected to an electric arc. The arc follower of the rod is a rod-shaped extension at the end of the metal contact rod and is generally somewhat smaller in diameter than the rod. When the contact rod is pulled from the contact member of the bore module, the resulting arcing passes between the follower and the bore lining. The exposure of the ablative material to arcing causes it to generate arc-extinguishing gases which rapidly extinguish the arc. This permits the connector to be utilized as a switch by being operated under live conditions, without creating a line-to-ground fault.
There is generally provided in the end of the contact rod a short, smaller diameter metal mounting pin which extends along the interior of the follower, either to provide a means for mounting the follower on the rod or to lend additional rigidity to the ablative material of the follower, if required. The pin cannot, however, extend the full length of the follower, as this would shunt the follower and defeat its function. Therefore, the pin terminates a short distance, about one cm (centimeter), from the follower end for insulation from the receiving contact. One problem with the above-described rod structure has been breakage of the follower tip, that portion of the follower extending beyond the end of the mounting pin. Such breakage can result in an arc from the mounting pin to the receiving contact, with resultant failure to interrupt the current.
A prior approach to the above problem has been the use of an insulating mounting pin which may extend the full length of the follower. Typically, such a pin is made of glass fibers bundled together in a resin binder. While such a structure does prevent breakage of the follower tip, it has been found that such a structure is more susceptible to failure at higher voltages than is the metal pin structure.